1. Field of the Invention
The present invention relates to a switching circuit, more particularly, to a switching circuit used for a measurement apparatus, a phase shifter, or a phased array system. Furthermore, the present invention also relates to a single pole double throw switch having two switching circuits used for a transceiver, and the like.
2. Description of the Related Art
Recently, a switching circuit is used in various apparatuses or systems, and a loss of signal transfer must be decreased regardless of the insertion of a switching circuit thereto. Note, when applying the switching circuit to an objective circuit, an impedance of the switching circuit must be matched with that of the objective circuit in order to decrease the loss of signal transfer. Namely, a characteristic impedance of the switching circuit must be matched with internal impedances of circuits connected to an input terminal and an output terminal of the switching circuit regardless of the ON or OFF state of the switching circuit.
For example, the prior art switching circuit comprises a first switching portion and a second switching portion. The first switching portion includes two FETs (Field Effect Transistors) connected in series between an input terminal and the second switching portion, and the second switching portion includes an FET and a resistor connected in series between a transmission line and the ground GND. Note, a first control signal is supplied to gate electrodes of the two FETs of the first switching portion, a second control signal is supplied to a gate electrode of the FET of the second switching portion, and the first control signal and the second control signal are complementary signals.
In this prior art switching circuit, a switching operation is carried out by the FETs of the first switching portion, and an impedance matching operation is carried out by the FET of the second switching portion. However, in the first switching portion of the switching circuit, two FETs are connected in series, and thus a loss of signal transfer becomes large by resistance components (resistive components) of the FETs.
Note, in the prior art, another switching circuit has been provided. For example, Japanese Unexamined Patent Publication (Kokai) NO. 1-264014 discloses a diode switching circuit.